With the increased use of resistance hybrids and various circuits incorporating resistance hybrids in the field of integrated analog circuitry, precise resistance adjustment in the resistance hybrid, without undue increase in hybrid circuit area, is of great importance.
One method for adjusting the electronic characteristics in semiconductor circuitry that includes analog circuits, involves the method of laser trimming, which is known in the art. Generally, laser trimming utilizes some of the fuse elements among those formed on a semiconductor wafer substrate and disconnects those elements by irradiating laser beams prior to dicing into chips (as shown in Japanese Laid-Open Patent Application No. 2000-323576). The semiconductor apparatuses are exemplified by incorporating a constant voltage generation circuit and a voltage detection circuit.
As illustrated in FIG. 7, for example, a constant voltage generating circuit 59 is provided to supply a stable power from DC power source 55 to load 57. The constant voltage generating circuit 59 includes an input terminal (Vbat) 61 to which the DC power source 55 is connected, a reference voltage (Vref) generator 63, an operational amplifier 65, a P-channel MOS transistor 67 (hereinafter referred to as “PMOS”) to serve as an output driver, and a voltage divider consisting of resistors R1 and R2 and an output terminal (Vout) 69.
The operational amplifier 65 is incorporated into the constant voltage generating circuit 59 such that the output terminal of the amplifier 65 is connected to the gate terminal of PMOS 67, the noninverting terminal is input with the reference voltage Vref from the reference voltage generator 63, and the inverting terminal thereof is input with the output voltage (Vout) divided by the resistors R1 and R2. The constant voltage generating circuit 59 is therefore controlled to bring the voltage divided by the resistors R1 and R2 to be equal to the reference voltage Vref.
FIG. 8 illustrates an exemplary electrical schematic diagram of a voltage detection circuit used in the prior art. An operational amplifier 65 is incorporated into the voltage detection circuit 71 for the inverting terminal of the amplifier 65 to be input with a reference voltage Vref from reference voltage generator 63.The voltage Vsens, which is input to an input terminal 73, is divided by the resistors R1 and R2. The divided voltage is then input to the noninverting terminal of the amplifier 65. In addition, the output of the amplifier 65 is forwarded to exterior by way of an output terminal 75.
The voltage detection circuit 71 is therefore operated such that the output level of the amplifier 65 remains high (“H”), if the voltage Vsens is high enough to bring the voltage, divided by the resistors, R1 and R2, higher than the reference voltage Vref. In contrast, the output level turns low (“L”), if the voltage Vsens decreases so as to bring the voltage, divided by the resistors, lower than the reference voltage. In the constant voltage generating circuit of FIG. 7 and the voltage detection circuit of FIG. 8, a scattering of the reference voltage Vref is encountered, primarily due to scattering of working parameters created during manufacturing process steps.
This scattering is compensated by means of a device, such as a resistance hybrid. The resistance value of the resistance hybrid can be adjusted by disconnecting its component fuse element and thereby serve as a voltage divider having desirable resistance value.
FIG. 9 is a circuit diagram illustrating dividing resistors used in the prior art. The resistance hybrid of FIG. 9 includes an Rbottom resistance element, which is coupled to (m+1) portions of setting resistance elements (RT0, RT1 . . . RTm), with m being a positive integer. An Rtop resistance element is connected in series to the setting resistance elements. The setting resistance elements RT0, RT1 . . . RTm are coupled in parallel to respective fuse elements RL0, RL1 . . . RLm. Such dividing resistors have been disclosed in Japanese Laid-Open Patent Application No. 2000-150799.
Using the above configuration of dividing resistors, the accuracy of the resistance ratio of the setting resistance can be improved. In practice, the accuracy is improved during fabrication by first forming a setting resistance element and a fuse element as a pair, and subsequently arranging a plurality of such pairs in ladder-shaped manner, as shown in FIG. 9. The desirable value of the resistance can be obtained by disconnecting arbitrary fuses which are properly selected among RL0, RL1 . . . RLm path by irradiating laser beams.
The dividing resistors of FIG. 9 may be utilized as the voltage divider, consisting of resistors R1 and R2 in the constant voltage generating circuit of FIG. 7, in which an end terminal on the Rbottom side is grounded. Furthermore, an end terminal on the Rtop side is connected to the drain of PMOS 67, and the junction terminal Node L, which is formed between Rbottom and RTO, is connected to the noninverting terminal of operational amplifier 15.
The voltage divider may also be used in the constant voltage generating circuit of FIG. 7, in which the end terminal of the resistance hybrid on the Rbottom side is grounded, the end terminal on the Rtop side is connected to the drain of PMOS 67, and the junction terminal Node M, which is formed between Rbottom and RTm, is connected to the noninverting terminal of operational amplifier 65.
The resistance hybrid of FIG. 9 may also be utilized as the voltage detection circuit illustrated in FIG. 8, in which the end terminal on the Rbottom side is grounded, the end terminal on the Rtop side is connected to a direct current source, and the junction terminal Node L is connected to the noninverting terminal of operational amplifier 65. The voltage divider may also be used in the voltage detection circuit, in which the end terminal on the Rbottom side is grounded, the end terminal on the Rtop side is connected to the direct current source, and the junction terminal Node M is connected to the noninverting terminal of operational amplifier 65.
In the noted laser irradiation method, however, there are encountered several drawbacks in disconnecting fuse elements such as (1) the costliness of laser trimming apparatus and high running costs for implementing the beam irradiation, (2) damage caused by the irradiation onto surrounding portions such as protective layer and substrate and (3) sputtering of fuse element materials and others in the vicinity of opening for the beam irradiation caused by the laser beam.